1. Field of the invention
The present invention relates to a vehicle cross member structure for a transmission and more specifically to a vehicle cross member structure capable of preventing a transmission or a propeller shaft from being protruded to a passenger compartment in an event of a collision.
2. Prior art
In a conventional motor vehicle, various cross members are utilized such as a cross member traversing between left and right front suspensions, a cross member traversing between left and right rear suspensions, a cross member traversing a transmission therebeneath and the like and the present invention relates to a cross member traversing a transmission among them. The object of such a cross member traversing a transmission (hereinafter, referred to as just "cross member") is to reinforce left and right side frames and at the same time to hold a power train including a transmission from underneath. Further, another object of the cross member is to protect an occupant from being injured by the transmission protruding into to the passenger compartment when an impact acts on the vehicle from outside. That is, the cross member is constituted such that the transmission including an engine is disconnected from the body so as to fall down in an event of an impact.
FIGS. 4 through 5b show a typical example of a cross member utilized in a power train system of a vehicle, in which a transmission 1 having an engine 3 in front and a propeller shaft in the rear is supported by a cross member 27 traversing between left and right side frames (not shown). The propeller shaft 2 comprises a first joint 1J connected to the output shaft of the transmission 1, a second joint 2J provided between a front shaft 2A and a rear shaft 2B and a third joint 3J connected to a rear differential and is supported by a floor panel therebeneath through a bracket 6 in the vicinity of the second joint 2J.
As shown in FIG. 5a, the cross member 27 has a U-shaped cross section downwardly opening. Further, as shown in FIG. 5c, the intermediate part of the propeller shaft 2A is supported by the bracket 6 which is mounted on the floor panel by mounting bolts through volt holes 6A, 6B opening in the front direction of the vehicle, so that the bracket 6 is detached from the mounting bolts when an impact is applied to the propeller shaft 2.
As shown in FIG. 6, when an impact F1 acts on the transmission 1, a moment M1 is caused, so as rotating the upper surface of the cross member 27 rear-downwardly, and a rear end of the transmission 1 and the first joint 1J move rear-downwardly by this moment, since the cross member 27 having a U-shaped cross section has a small torsional rigidity. As a result, the front shaft 2A of the propeller shaft 2 is inclined rear-upwardly. Thereby an upward force F2 is caused at the intermediate point of the propeller shaft 2 to push the second joint 2J upwardly.
In order to obviate such a defect, Japanese Examined Utility Model Application No. Jitsu-Ko-Hei 2-45062 and Japanese Patent Application Laid-open No. Toku-Kai-Hei 6-166379 were proposed.
As well known, since the closed cross section structure has a large resistance to torsion, downward displacements of the rear end of the transmission 1 and the first joint 1J and the inclination of the front shaft 2A of the propeller shaft 2 are smaller than those of the U-shaped cross section structure. Thereby the front shaft 2A of the propeller shaft 2 is prevented from being projected toward the floor panel.
However, such a cross member structure as relying only upon a resistance to torsion is still insufficient for stably displacing the transmission rearwardly when an impact is applied to the transmission.